This application claims priority to German patent application 100 15 430.1, filed Mar. 28, 2000. The entire content thereof is incorporated herein by reference.
1. Field of the Invention
The present invention relates to capacitive sensors for detecting surface condensation.
2. Related Art
Sensors are often used to detect incipient moisture on automotive windshields. These sensors may be used to detect condensation on the surface of a windshield, and by analyzing signals generated by the sensors, it is possible to take measures to reduce the condensation.
Such a sensor is described in German Patent Application DE 197 080 53 A1. The patented sensor includes a carrier layer onto which is applied a metal layer as an interdigital structure, thereby forming a capacitor. A temperature-dependent resistor that is integrated into the capacitor is also used simultaneously as a temperature sensor and as a heating sensor. In addition to a passivation layer, an additional layer that promotes moisture condensation is applied to the carrier layer. Nuclei of condensation, i.e., irregularities at which condensation of moisture begins, are integrated into this additional layer.
However, the known device has a specific disadvantage. In particular, the device does not readily achieve a uniform water film formation, which accurately indicates the formation of condensation. Instead, as condensation beings (nuclei of condensation), droplet-like moisture forms having an irregular formation, which thus reduces the sensitivity of the sensor.
The object of this invention is to provide a generic sensor, which has a greater sensitivity.
The object of the present invention is achieved by treating the surface of a passivation layer applied over an interdigital capacitor in a controlled manner, to increase the surface energy or surface tension. This eliminates having to use an additional layer with condensation nuclei. Therefore, moisture condensation molecules can develop anywhere on the surface, causing a change in the capacitance of the interdigital capacitor at any point on the surface.
The surface is preferably prepared by applying a hydrophilizing agent to produce a hydrophilic layer applied to the passivation layer. The hydrophilic layer is preferably applied using a dipping or spraying method.
The advantageous effects of the present invention include better feed through of an electric field due to the moisture, an improvement in uniform water condensation at the start of the condensation of moisture, and the development of a continuous film of water.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.